The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
The present invention relates to a deforming charge assembly and method of making same and more particularly to a deforming charge assembly which reduces the danger of explosion by the charge assembly.
Ordinance items such as loaded charge assemblies, for example those used in rocket motors, warheads and bombs, present an extreme hazard in the event of xe2x80x9ccook offxe2x80x9d which is defined for purposes of the subject application as detonation or deflagration of the main explosive charge of the item due to an accidental fire. The transportation and storage of charge assemblies, loaded with an explosive, frequently requires placing them in environments which have a high probability of being in the proximity of open flames. For example, loaded charge assemblies are frequently placed on the flight deck of a naval ship where an aircraft fuel tank is also present. If accidental rupture of the fuel tank occurs, fuel spreads over the flight deck. A fire that results upon ignition of the spilled fuel can subject the loaded charge assemblies to high temperatures along with a high risk of ignition of the explosive material in the charge assemblies. The rapid internal pressure buildup in the loaded charge assemblies will result in case rupture and explosion with catastrophic results, including costly equipment losses and potential loss of life.
Efforts have been made to modify charge assemblies to preclude explosive behavior of the charge assembly when loaded with an explosive material or to extend the time prior to violent reaction of the loaded charge assembly to a fire. It is desirable to provide an economical, reliable and tailorable charge assembly which provides the necessary structural integrity under normal conditions essential to its primary mission, while allowing structural degradation when the assembly reaches a predetermined abnormally elevated temperature which is below the auto ignition temperature of the explosive in the charge assembly. Such a charge assembly design renders the loaded charge assembly incapable of sustaining sufficient internal pressure to destructively detonate the charge assembly.
With the advent of plastic and other fibers, various materials have been used to form ordinance devices. For example, U.S. Pat. No. 2,872,865 discloses a woven fiber glass sleeving impregnated with plastic material. U.S. Pat. No. 5,369,955 shows a filament of polyolefin or polyethelene wound on a mandrel in a number of plies and impregnated with a matrix material curable by radiation. U.S. Pat. No. 5,170,007 discloses a sheet of material woven from a composite fiber reinforced thermoplastic, such as polyethersulfonegraphite fiber, rolled into a cylinder. An adhesive, having a breakdown temperature less than the autoignition temperature of the propellant in the cylinder, is used to hold the sheet in the cylindrical form and release before the propellant reaches its autoignition temperature.
U.S. Pat. No. 5,035,180 discloses an ordinance venting system having a number of holes in the ordinance casing covered by thermal metallic patches which expand at a different rate than the casing and open the vent holes when subjected to heat.
U.S. Pat. No. 3,992,997 shows an insulated warhead casing having a metallic tube surrounded by an ablative material such as cork, carbon or TEFLON and an outer fire resistant layer of glass fiber material impregnated with curable epoxy adhesive. U.S. Pat. No. 5,125,179 teaches a gun barrel formed from a ceramic material sections surrounded by an outer sleeve of braided graphite composition structure or a graphite fiber/epoxy composite wrapped about the ceramic sections. Other warhead designs used a graphite epoxy material, wound in a thin cylinder, to contain an explosive billet which is removed during depot maintenance of the missile.
U.S. Pat. No. 4,646,615 discloses a barrel section for a lightweight firearm manufactured by positioning epoxy treated carbon fibre rovings in grooves in a mandrel with an inner mandrel supporting the rovings which are at a slight helical angle to form the rifling of the barrel. The grooves have a slight narrowing towards the center of the barrel to facilitate removal of the grooved mandrel after formation of the barrel. A carbon fibre material treated with an epoxy resin is then wound around the mandrels and rovings in the desired angle and layers. Preferably the first four layers are hoop wound at a helix angle as close to 90 degrees as possible within the remaining layers wound according to a formula.
Deforming charge assemblies of the type provided by the present invention have been made with strips of relatively insensitive Dupont LF-2 Detasheet, separated by sympathetic detonation barriers, applied around the portion of the warhead circumference on the side to be deformed. In a system application, Detasheet would be placed around the entire warhead. The number of strips and barriers would be determined by the number of firing directions that a candidate system could support. The barrier would confine the detonation to those sectors specifically selected by the target detection device (TDD), and fired and initiated by the electronic safe arm device (ESAD) and the warhead initiation system (WIS).
Safety requirements dictated that an insensitive form of Detasheet be used in any tactical system. When the insensitive LF-2 Detasheet became unavailable, alternate designs using insensitive explosive as a means of deforming the warhead had to be devised. More sensitive Detasheet was available and could be used to complete development, but it was too sensitive for tactical applications. Also, when producibility and depot maintenance were considered, the use of discrete strips of Detasheet with barriers between them was not an acceptable design. Graphite-epoxy materials, wound in a thin cylinder, have been used to contain explosive billets which are removed during depot maintenance of the missile.
It is therefore an object to provide a deforming charge assembly loaded with an explosive that can be sized to duplicate the performance characteristics of Detasheet and which resolves the problems inherent with separate pieces of Detasheet and barriers. It is a further object to provide a deforming charge assembly that may be efficiently mass produced and that may be efficiently explosively loaded by the extrusion process. It is a further object to provide a graphite housing of the deforming charge assembly to aid in meeting Insensitive Munitions (IM) requirements.
The present invention provides a deforming charge assembly which as an inner and an outer cylinder formed from carbon fiber. Each of the inner and outer cylinders have an inner circumference surface having an inner diameter, and an outer circumference surface having an outer diameter. The inner diameter of the outer cylinder is greater than the outer diameter of the inner cylinder. Each of the inner and outer cylinders have a first layer of circumferentially wound carbon fiber, a second layer of unidirectional carbon fiber sheet and a plurality of layers of carbon fibers circumferentially wrapped around the second layer. A plurality of sympathetic detonation barrier members are provided and have an inner surface in contact with the outer circumference surface of the inner cylinder and an outer surface in contact with the inner circumference surface of the outer cylinder which form a plurality of annular cavities.
The deforming charge assembly is formed by the method of circumferentially winding a carbon fiber around an inner mandrel to form a first layer of the inner cylinder, wrapping a unidirectional carbon sheet around the first layer of the inner cylinder to form a second layer of the inner cylinder, circumferentially winding a carbon fiber around the second layer of the inner cylinder to form a plurality of outer layers, coating the inner cylinder with epoxy resin. The outer mandrel is then positioned around the inner cylinder and in contact therewith. The outer mandrel has slots extending from one end of the outer mandrel towards the other end of the outer mandrel. Steel sympathetic detonation barrier strips and strips of TEFLON on each side of the barrier strip are positioned in each of the slots in the outer mandrel. The method then provides for circumferentially winding a carbon fiber around the outer mandrel to form a first layer of an outer cylinder, wrapping a unidirectional carbon sheet around the first layer of the outer cylinder to form a second layer of the outer cylinder, circumferentially winding a carbon fiber around the second layer of the outer cylinder to form a plurality of outer layers, coating the outer cylinder with epoxy resin, and removing the outer mandrel from between the inner and outer cylinders and the inner mandrel from the inner cylinder.
An explosive, such as PBXW-128, is injection loaded into the annular cavities and is sized to duplicate the performance characteristics of Detasheet which resolves the problems inherent with separate pieces of Detasheet and barriers. The present invention provides a deforming charge assembly which may be efficiently mass produced and that may be efficiently explosively loaded by the extrusion process. A deforming charge assembly is also provided by the present invention having a graphite housing which aids in meeting Insensitive Munitions (IM) requirements. In addition to light weight and strength, graphite material is electrically conductive, thereby eliminating the electrostatic hazard often associated with composites and explosives.